A typical bipolar electrolytic cell comprises a number of bipolar cell units arranged in series. Each unit comprises parallel anode and cathode plates spaced by a partition or centerboard which is attached to an outer frame or peripheral flange. In each unit, the centerboard may comprise a form sustaining steel plate confronting and spaced from the cathode plate, and a titanium sheet lined or bonded to the steel plate and confronting and spaced from the anode plate. A low resistance electrical connection between the anode and cathode plates may also include means for supporting the plates in parallelism with each other.
In a typical construction illustrated in U.S. Pat. No. 4,111,779, the anode plate is a titanium foraminous sheet or woven wire mesh spaced from the anode sheet of the partition by a plurality of titanium ribs welded to both the anode plate and titanium sheet. The cathode plate comprises a steel foraminous or woven wire sheet spaced from the steel partition plate by a plurality of steel ribs welded to both the steel partition plate and cathode plate. Inasmuch as the partition frequently has a slight initial bow which tends to increase when welded to the titanium and steel ribs, the outer edges of the ribs welded to the cathode and anode plates are frequently not parallel. It is important to maintain closely spaced parallelism between the cathode and anode plates of adjacent bipolar units in order to achieve a uniform potential gradient and current flow therebetween throughout their surface areas. If the desired parallelism is not closely maintained, the space between these plates must be sufficiently large to avoid electrical contact and short circuits, resulting in an undesirably low potential gradient between various portions of the plates. Also the resulting nonuniform distribution of current flow and electrolytic action can cause increased cell voltage, localized overheating, and shortened cell life. In order to minimize such defects, the edges of the ribs remote from the partition are machined to the desired parallelism before being welding to the anode and cathode plates. The precision machining however is time consuming and costly.
U.S. Pat. No. 4,194,670 to Ichisaka et al provides a bipolar cell free from the above noted defects and wherein the anode and cathode plates are supported in parallelism with each other. In that construction, the various ribs welded to their respective anode or cathode plate are also welded at adjusted positions to a number of spaced connectors which in turn are welded to the partition. Prior to welding the ribs to their respective connectors, the ribs are adjustably supported in a welding fixture to assure that the outer edges of the ribs that will be subsequently welded to the associated anode or cathode plate will support that plate in a predetermined plane and at a predetermined distance from the partition. Thereafter the associated plate, the anode plate for example, is welded to the outer edges of the titanium ribs and supported thereby in the predetermined plane. The steel cathode ribs are similarly supported in adjusted positions by means of welding fixtures and thereafter welded to the various connectors which have previously been welded to the steel plate of the partition. The cathode plate is then welded to the outer edges of the steel ribs remote from the partition to obtain the desired horizontal spacing between the anode and cathode plates.
Although it is alleged in the specification of U.S. Pat. No. 4,194,670 that the desired parallelism between the anode and cathode plates is obtained, it is technically difficult to achieve continuous resistance welding of the anode and cathode plates to their respective ribs between the adjacent connectors because, unlike the condition prevailing in U.S. Pat. No. 4,111,779, the ribs are spaced from the partition at the regions thereof between the connectors. In consequence thermally induced warping or buckling of the anode and cathode plates from their desired condition of parallelism occurs at the regions that are not positively welded to their supporting ribs. Furthermore, the resistance welding of the anode plate to its titanium ribs results in electrical sparking in the gap between the ribs and the titanium sheet of the partition with consequent damage to the thin anode partition sheet.
Important objects of the present invention are to avoid the above noted objections and to provide an improved bipolar electrolytic cell and method of construction whereby the anode and cathode plates may be welded to their respective anode and cathode ribs before these ribs are secured by their respective connectors to the partition.
Another important object is to provide an improved bipolar cell of the type described comprising a plurality of anode and cathode connectors removably secured to the anode and cathode sides respectively of the centerboard or partition. A plurality of titanium anode plate supporting ribs are spaced across the surface of the anode plate and arranged at predetermined positions of adjustment with respect to the titanium connectors and welded thereto at the adjusted positions whereat the outer edges of the ribs define a predetermined plane for supporting the anode plate. The anode plate is resistance welded to said outer edges of the titanium ribs and is thus supported in a predetermined plane spaced from the partition. Similarly the cathode plate is resistance welded to a plurality of steel cathode ribs spaced over the surface of the cathode plate. Each cathode rib is welded at a predetermined adjusted position to each of a plurality of connectors which in turn are removably secured to the partition, whereby the cathode plate is also supported at a predetermined location in parallelism with the anode plate.
Other objects are to provide an improved bipolar cell that enables a preferred method of construction to assure positive support for the anode and cathode plates of adjacent cell units in precisely spaced parallelism with each other, and to provide an improved method for fabricating such a cell wherein the anode and cathode connectors are first removably secured to the centerboard or partition. Thereafter the partition (attached to the connectors) and the plate supporting ribs are supported by a welding jig in predetermined adjusted positions such that the outer edges of the ribs remote from the partition define predetermined parallel planes for supporting the anode and cathode plates at their desired parallel positions. The ribs are then welded at their adjusted positions to their respective connectors, whereupon the connectors (welded to the ribs) are removed from the partition. The anode and cathode plates are then welded to the outer edges of their respective ribs by conventional resistance welding procedure. The assemblies of the ribs welded to their respective anode and cathode plates and to their respective anode and cathode connectors are then assembled to the partition by virtue of the removably attachable connectors.
Another important object of this invention is to provide an improved bipolar cell with removably attachable connectors which enable the electrode plates to be disassembled from the centerboard of the cell frame for repair or recoating and thereafter reassembled to the centerboard.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.